Spectrophotometric and Chromatographic Assessment of Total Polyphenol and Flavonoid Content in Rhododendron tomentosum Extracts and Their Antioxidant and Antimicrobial Activity

Abstract

In the literature, the chemical composition of <i>Rhododendron tomentosum</i> is mainly represented by the study of isoprenoid compounds of essential oil. In contrast, the study of the content of flavonoids will contribute to the expansion of pharmacological action and the use of the medicinal plant for medical purposes. The paper deals with the technology of extracts from <i>Rh. tomentosum</i> shoots using ethanol of various concentrations and purified water as an extractant. Extracts from <i>Rh. tomentosum</i> were obtained by a modified method that combined the effects of ultrasound and temperature to maximize the extraction of biologically active substances from the raw material. Using the method of high-performance thin-layer chromatography in a system with solvents ethyl acetate/formic acid/water (15:1:1), the following substances have been separated and identified in all the extracts obtained: rutin, hyperoside, quercetin, and chlorogenic acid. The total polyphenol content (TPC) and total flavonoid content (TFC) were estimated using spectrophotometric methods involving the Folin-Ciocalteu (F-C) reagent and the complexation reaction with aluminum chloride, respectively. A correlation analysis was conducted between antioxidant activity and the polyphenolic substance content. Following the DPPH assay, regression analysis shows that phenolic compounds contribute to about 80% (<i>r</i>² = 0.8028, <i>p</i> < 0.05) of radical scavenging properties in the extract of <i>Rh. tomentosum</i>. The extract of <i>Rh. tomentosum</i> obtained by ethanol 30% inhibits the growth of test cultures of microorganisms in 1:1 and 1:2 dilutions of the clinical strains #211 <i>Staphylococcus aureus</i> and #222 <i>Enterococcus</i> spp. and the reference strain <i>Pseudomonas aeruginosa</i> ATCC 10145.